Various thin-films and other structures are formed on the surfaces of semiconductor wafers during the several phases of the integrated circuit fabrication processes. In a typical case, the wafers to be processed are disposed into so-called boats, and the wafer-loaded boats are placed on a so-called boat loading mechanism operable to transfer the tube-load of wafer-loaded boats into the thermal reaction chamber of a processing furnace tube. One or more reactants in gas phase, controllably released in the thermal reaction chamber, pyrolically decompose and are surface catalyzed by the wafers to form the intended thin-film structures thereon. The boat loading mechanism is operative after selected thin-film formation to remove the tube-load of wafer-loaded boats from the thermal reaction chamber, and the same or another process is repeated on the same or another tube-load of wafer loaded boats.
Typically, several processing furnace tubes are arrayed in a vertically stacked relation, and each is provided with a separate boat-loading mechanism. The plural processing furnace tubes are operable in parallel so that the system throughput is limited theoretically only by the number of processing furnace tubes.
To realize the theoretically achievable throughout in a practicable automated furnace system, several objectives become important. Not only must several tube-loads of wafers be available at a given time, but also they should be made available in such a way that operator assistance is minimized and operator intervention is as infrequent as possible. After wafer processing, several tube-loads of coated wafers must be received and expeditiously stored until an operator or some mechanism provided therefor removes them from the system. Further, the several tube-loads of wafers must be maintained in a very clean state, so that they are not contaminated either by air-borne contaminates during transfer or by cross-contamination from a prior tube-load of already processed wafers.